Author Topic: Current progress on my 14-stage CW multiplier  (Read 588 times)

Offline MRMILSTAR

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Current progress on my 14-stage CW multiplier
« on: January 05, 2021, 06:02:07 AM »
Here is my current progress on the 14-stage half-wave CW multiplier that I am building. This is the multiplier stack consisting of TDK doorknob capacitors, resistors, and diodes. It is 39" tall. The stack will be all under oil in a 4" diameter clear PVC tube. Everything is mounted on an acrylic carrier. This was my first experience with cementing acrylic and it turned out well. The good part about cementing acrylic is that you get immediate bonding. The bad thing is that it is very unforgiving of placement errors. Once you apply the cement, it is stuck and not coming off or moving. You have about one second of work time. So measure twice, cut once.

The specs are:

* Capacitance: TDK doorknob type, 28 total, each with 1.7 nF and rated for 30 KV
* Diodes: 20 KV each rated for 30 ma, each string consisting of 3 diodes in series resulting in a 60 KV rated diode string
* Resistance: 4.3M ohms total consisting of 28 resistors in series with each rated for 10 KV and 150K ohms

The design output voltage is about 250 KV. The power supply will be two AC flyback transformers in parallel. The resistors are mounted in a spiral at the top of the stack.

Also shown is the bottom mount for the tube. It shows the two copper electrodes which the springs on the bottom of the multiplier stack will make contact with in order to establish connection with the HV power supply.
« Last Edit: January 10, 2021, 10:27:20 PM by MRMILSTAR »
Steve White
Cedar Rapids, Iowa
Retired electrical engineer

Offline Da_Stier

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Re: Current progress on my 14-stage CW multiplier
« Reply #1 on: January 06, 2021, 11:35:33 AM »
Nice build, it looks very clean.
I like the double sided staggered design, it makes it really compact.
Will you glue it into the acryllic tube in the end?

This might be a pretty dumb question, but what do you need the resistors for, current limiting?



Greetings,
Michael

Offline MRMILSTAR

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Re: Current progress on my 14-stage CW multiplier
« Reply #2 on: January 06, 2021, 03:34:30 PM »
Thanks for the compliments. I am designing this multiplier to be easily serviceable so the stack will not be permanently attached to the tube. The top of the tube will have a screw-on lid so that I can remove the multiplier stack at any time if the need arises.

The resistor string is for current limiting otherwise the diodes could be fried from excessive current.
« Last Edit: January 06, 2021, 08:41:38 PM by MRMILSTAR »
Steve White
Cedar Rapids, Iowa
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Offline Weston

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Re: Current progress on my 14-stage CW multiplier
« Reply #3 on: January 07, 2021, 06:52:06 AM »
Looks great! Whats your plan for electrical feedthroughs on the bottom that will not leak oil?

Offline MRMILSTAR

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Re: Current progress on my 14-stage CW multiplier
« Reply #4 on: January 07, 2021, 05:16:12 PM »
I gave the feed-throughs a lot of thought. I have already built the base. I drilled and tapped two holes in the bottom of a PVC end-cap. I then threaded banana jack screw terminals into the tapped holes. These terminals are then attached by wires to a custom contact plate at the bottom of the PVC end-cap with 2 copper electrodes for the spring contacts of the multiplier stack to rest on. I then poured 2-part epoxy into the bottom of the end cap so that the threads and holes were covered and sealed. I don't think that there is any way that this will leak. I added a few pictures to my previous posting which I hope will make this clear.
« Last Edit: January 10, 2021, 10:20:48 PM by MRMILSTAR »
Steve White
Cedar Rapids, Iowa
Retired electrical engineer

Offline Mads Barnkob

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Re: Current progress on my 14-stage CW multiplier
« Reply #5 on: January 08, 2021, 10:44:46 AM »
What are you going to power with this CW multiplier?

Very nice construction with all sharp corners avoided, very nice. I like the way you did your output resistance and thought about using the same for my marx generator tower project.

It has been a project that I made some parts for and bought the components, but kind of never got to put it all together, I just checked the files, that was back in 2008 :o


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Offline MRMILSTAR

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Re: Current progress on my 14-stage CW multiplier
« Reply #6 on: January 08, 2021, 04:40:52 PM »
Thanks Mads. I've had the parts for this sitting around for about 2 years so I finally decided to make this my winter project. This multiplier project only got started because I got a fantastic deal a few years ago on the 28 TDK capacitors from a TCML member who was liquidating his excess stuff. I had to find something useful to do with these 28 capacitors! That's why its a 14-stage multiplier.

I entertained several ideas for building the HV resistor array. One idea looked sort of like a circular  "Pan's pipe" but it took up a lot of linear space and would have resulted in an even taller tube. I also considered putting the resistance in a separate discharge terminal tower but I decided that I wanted everything in the same tube because I didn't want to deal with a second oil-filled tube. I finally arrived at this spiral chain idea as the best compromise of HV capability versus size.

Even though it will all be under oil I have tried my best to avoid sharp edges and corners and even used solder blobs where possible. It was a real challenge on the diode strings which have to fit closely to the capacitors.

My only application right now is just to demonstrate a continuous HV streamer to a discharge terminal.

You should finish that Marx generator Mads. Your design looks very interesting. I have a 20-stage Marx that emits very loud 12 inch discharges about every 2 seconds very consistently and even longer less consistently. It is battery powered with two 12-volt UPS batteries in series. I have not yet had to re-charge the batteries after two years of infrequent operation.
« Last Edit: January 10, 2021, 10:23:01 PM by MRMILSTAR »
Steve White
Cedar Rapids, Iowa
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Offline Da_Stier

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Re: Current progress on my 14-stage CW multiplier
« Reply #7 on: January 08, 2021, 05:10:36 PM »
After looking through the pictures again on a bigger screen, I noticed how clean your cuts are.
Did you lasercut the acrylic?


Greetings,
Michael

Offline MRMILSTAR

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Re: Current progress on my 14-stage CW multiplier
« Reply #8 on: January 08, 2021, 05:56:55 PM »
I used a band saw for the straight cuts followed by wet-sanding of the cut edges with 400-grit sandpaper. I used a circular saw for the round piece again followed by wet sanding of the cut edge. I used my milling machine to cut the slots for the resistors. The milling machine cutter produces a naturally smooth cut.
« Last Edit: January 09, 2021, 05:51:45 AM by MRMILSTAR »
Steve White
Cedar Rapids, Iowa
Retired electrical engineer

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Re: Current progress on my 14-stage CW multiplier
« Reply #8 on: January 08, 2021, 05:56:55 PM »

 


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